Projection ion beam machining apparatus

ABSTRACT

In a projection ion beam machining apparatus having a liquid metal ion source, a combination of two or three electrostatic lenses arranged between the liquid metal ion source and a sample and a stencil mask exchangeably arranged in the combination of the electrostatic lenses, when a distance from substantial center of the electrostatic lens most proximate to the ion source and an ion emitting portion of the ion source is designated by Lo, a distance from the substantial center of the electiostatic lens most proximiate to the sample and the surface of the sample is designated by Li and a distance between the substantial centers of the two lenses is designated by L, by making a value of (L/Lo)(L/Li) equal to or larger than 400, current density on the sample of ion beam accelerated to several 10 kV for projecting a pattern of a stencil mask can be made equal to or larger than 20 mA per 1 square cm and resolution of edge can be made equal to or smaller than 0.2 μm when the size of the ion beam is 5 μm. As a result, a region having a size equal to or smaller than several 10 μm can be machined at speed several times or more as fast as that of FIB having equivalent machining accuracy.

TECHNICAL FIELD

The present invention relates to an ion beam machining apparatus fordirectly machining a very small portion of an electronic part, such as asemiconductor or the like, and, more particularly, to an ion beammachining apparatus which is capable of high speed machining by using aprojection ion beam.

BACKGROUND OF THE INVENTION

In this technical field, there is a direct machining technologyutilizing sputtering produced by irradiating a Focused Ion Beam (FIB) ona sample, and there is a method of observing a section of asemiconductor device or modifying wirings by using the machiningtechnology (Japanese Unexamined Patent Publication No. 02-295040).

As is well known, a FIB is formed by focusing an ion beam emitted from aliquid metal ion source onto a sample using an electrostatic lens systemto thereby produce an image of the ion source. The image of the ionsource is very small and, therefore, there is provided a beam diameterdetermined mainly by aberration of the electrostatic lens system, andthe size of which practically falls in a range of several 10 nm throughseveral μum. Further, in the application thereof to direct machining,generally the acceleration voltage is set to 20 through 60 kV and thecurrent falls in a range of several pA through 10 nA. The FIB can beirradiated to an arbitrary point and scanned in a region of about 1 mmat maximum on a sample by using an electrostatic deflector. In thiscase, in the case of using a FIB, due to the aberration of theelectrostatic lens, when the current is increased, the beam diameter isenlarged. When the beam current reaches several nA, blur is rapidlyenhanced due to the spherical aberration of the electrostatic lens andthe current density is reduced. Therefore, the beam diameter is switchedby changing the aperture or the focused state in accordance with themachining area and machining accuracy such that the machining speed isreduced as little as possible. Particularly, in forming a cross sectionof a sample for observation by a scanning electron microscope (SEM), asshown in FIG. 7(a), which is most generally carried out by machiningusing a FIB, a hole having a rectangular region of about 10 μm is dug toa similar degree of depth and machining is carried out by switching thebeam to a slender beam successively twice through three times in orderto finish only a face for observing the cross section. Further, asimilar operation is carried out in forming a wall of a sample forobservation by a transmission electron microscope (TEM), as shown inFIG. 7(b).

Further, there is known projection ion beam technology capable offorming a pattern with high accuracy. According to Japanese UnexaminedPatent Publication No. 2-65117, the beam is used in lithography and anarea having a size of several 10 mm is exposed by an accuracy of sub μm.It is regarded that, although the projection ion beam is suitable forirradiating a large area with a high accuracy, the beam is not suitablefor an application which needs a high current density to carry outdirect sputtering machining. In this case, a technology for carrying outhigh accuracy machining by applying an FIB apparatus to a projection ionbeam apparatus is disclosed in Japanese Unexamined Patent PublicationNo. 8-213350. In accordance with this technology, the beam current is 10nA at most, similar to that in a FIB, since the constitution of the FIBapparatus is used and there is no description with regard to atechnology enabling high speed machining which can replace the FIB.

As described above, there is no known ion beam forming technologycapable of realizing a machining speed exceeding that of a FIB and whichis capable of forming a region of several 10 μm or smaller with anaccuracy of sub μm.

It is an object of the present invention to provide a projection ionbeam machining apparatus which is capable of machining a region having asize of several 10 μm or smaller, at high speed, and of processing anedge of the region with high accuracy by using an ion beam projecting apattern of a member having an opening portion (stencil mask).

SUMMARY OF THE INVENTION

The present invention is based on optimum conditions in the design of anelectrostatic lens system and indispensable matters in constituting anapparatus which we have found for constituting a projection ion beamapparatus capable of machining at high speed and with high accuracy incomparison with a FIB. The optimum conditions in the design of anelectrostatic lens system referred to here are mainly optimum ranges ofa distance between an ion source and a lens proximate to the ion source,a distance between a sample and a lens proximate to the sample and adistance between these two lenses. To satisfy such design conditions,specific combinations with regard to the constitution of the apparatusare needed.

An explanation will be given of conditions in the design of anelectrostatic lens system. First, for simplicity an investigation hasbeen made of a case in which two electrostatic lenses, that is, a lens 1proximate to an ion source and a lens 2 proximate to a sample are used,as shown in FIG. 8(a) and FIG. 8(b). FIG. 8(a) shows a case of forming aFIB in which the intensities (inverse number of focal length) of the twolenses are adjusted such that an image of the ion source is formed onthe sample by the ion beam. FIG. 8(b) shows a case of forming aprojection ion beam in which the strength of the lens 2 is adjusted suchthat an image of a stencil mask is formed on the sample by the ion beam.In this case, the lens 1 is an illumination lens for adjusting theamount of irradiating ions which impinge onto the stencil mask, and thelens 1 converges the ion beam to a center of the lens 2. Further, thelens 2 is a projection lens for projecting the image of the mask ontothe sample, and the lens 2 converges the ion beam radiated fromrespective points of the stencil mask onto the sample along trajectoriesshown as dashed lines in FIG. 8(b).

The following has been found by investigating characteristics of the twoion optical systems by calculation. That is, when the distance betweenthe ion source and the center of the lens 1 is designated by notationLo, the distance between the sample and the center of the lens 2 isdesignated by notation Li and the distance between the centers of thelens 1 and the lens 2 is designated by notation L, in the case of FIG.8(a), the current density of the FIB on the sample is proportional to1/(Lo×Li). In the meantime, in the case of FIG. 8(b), the currentdensity of the projection ion beam on the sample is proportional to thesquare of L/(Lo×Li). That is, when a comparison is made with the samelens arrangement, a ratio of the current density of the projection ionbeam as compared with the current density of the FIB is proportional to(L/Lo)(L/Li). Further, in the case of the projection ion beam, when thecurrent density is increased, distortion is increased in proportion tothe ninth power of Lo and the third power of Li even in a pattern havingthe same size and the same current density.

It has been found from the foregoing results that in the electrostaticlens system of the projection ion beam apparatus according to thepresent invention, it is necessary to increase L and reduce Lo and Li,and more particularly to reduce Lo to minimize the distortion to adegree which is not conceivable in the case of a FIB apparatus. For suchpurpose, it is indispensable to arrange all of the elements of the ionoptical system, other than the electrostatic lenses, between theelectrostatic lenses. In the meantime, when L is increased, the accuracyof the setting voltage of a lens power source necessary for adjustingthe strength (inverse number of focal length) of the electrostatic lensproximate to the ion source becomes more and more severe and,accordingly, it has been found that there is an upper limit for L.However, it has been also found that this restriction can be alleviatedand L can be effectively increased when the electrostatic lenses areincreased in three stages. Further, it has been found that a focusingcondition of the ion beam for minimizing the distortion of the projectedpattern on the sample differs for each size of the pattern of the mask.Therefore, it has been found that there is needed a mechanism capable ofswitching the intensities of the respective electrostatic lenses incooperation with the size of the pattern of the mask. Theabove-described discussion assumes that the ion beam passes on thecentral axes of the lenses, and it has been found that when the ion beamis disposed off of the axes (particularly in the lens proximate to thesample), the position of the projection ion beam on the sample isshifted and an edge of the pattern is significantly distorted. Hence, ithas been found that a deflector for always accurately guiding the ionbeam on the axes is indispensable. Further, it has been found that whenthe strength of the lens for projecting the mask is inaccurate, the sizeof the pattern of the ion beam on the sample is varied. Hence, it hasbeen found that in order to confirm the condition of the projectionlens, means for effectively moving the ion source, that is, a deflectorarranged on the ion source side of the mask, is indispensable.

Specifically, the problem is solved by a projection ion beam machiningapparatus provided with an ion source, a stage for holding a sample, afirst electrostatic lens disposed between the ion source and the stageand provided on the side of the ion source, a second electrostatic lensprovided on the side of the stage, a mask having an opening portionprovided between the first electrostatic lens and the secondelectrostatic lens, a first electrostatic deflector provided between themask and tile first electrostatic lens and two stages of electrostaticdeflectors provided between the second electrostatic lens and the mask.

Further, in the above-described projection ion beam machining apparatus,the first electrostatic lens is a lens synthesized by arranging anacceleration lens having two electrodes and an Einzel lens having threeelectrodes (lens in which potentials of the electrodes at both ends arethe same) successively from the side of the ion source.

Furthermore, in the above-described projection ion beam machiningapparatus, an aperture is arranged between the acceleration lens havingthe three electrodes and the Einzel lens having the three electrodes.

Furthermore, in the above-described projection ion beam machiningapparatus, the second electrostatic lens is an Einzel lens.

Furthermore, the above-described projection ion beam machining apparatushas an electrostatic deflector for blanking the ion beam on the side ofthe ion source of the second electrostatic lens and a fixed aperturearranged on the side of the sample of the electrostatic deflector.

Furthermore, in the above-described projection ion beam machiningapparatus, the ion source is a liquid metal ion source.

Furthermore, in the above-described projection ion beam machiningapparatus, the sample is machined with a high sputtering efficiency bymaking the acceleration voltage of the ion beam equal to or higher than20 kV and equal to or lower than 60 kV.

Further, in the above-described projection ion beam machining apparatus,the mask is provided with a group of a plurality of selectable openingsand a control system for controlling operation of the electrostatic lenssystem is provided with means for storing two sets or more of controlparameters and means for changing the sets of the control parameters forrespective ones of the openings of the mask.

Furthermore, in the above-described projection ion beam machiningapparatus, at least one of the openings of the mask is formed in acircular shape.

Further, the above-described projection ion beam machining apparatus hasmeans for detecting secondary particles (secondary elections, secondaryions or secondary beam) emitted from the sample, means for scanning theion beams on the sample by using the two stages of electrostaticdeflectors provided between the second electrostatic lens and the maskor the electrostatic deflector provided between the mask and the firstelectrostatic lens and means for forming and displaying an image of thesample by using an output signal provided from the means for detectingthe secondary particles in synchronism with the scanning.

Furthermore, the above-described projection ion beam machining apparatushas means for designating a position for irradiating the projection ionbeam onto the sample by using a display of a one-dimensional ortwo-dimensional image of the sample.

Furthermore, the problem is solved by a projection ion beam machiningapparatus which is provided with a liquid metal ion source, a stage forholding a sample, a combination of two or three electrostatic lensesarranged between the ion source and the sample and a mask having openingportions disposed in the combination of the electrostatic lenses,wherein, when the distance between substantial center of theelectrostatic lens most proximate to the ion source and an ion emittingportion of the ion source is designated by notation Lo, the distancebetween a substantial centers of the electrostatic lens most proximateto the sample and a surface of the sample is designated by notation Liand the distance between the substantial centers of the two lenses isdesignated by notation L, a value of (L/Lo)(L/Li) is equal to or largerthan 400.

Further, the problem is solved by a projection ion beam machiningapparatus which is provided with a liquid metal ion source, a stage forholding a sample, a combination of two or three electrostatic lensesarranged between the ion source and the sample and a mask having openingportions arranged in the combination of the electrostatic lenses,wherein the distance between an ion emitting portion of the ion sourceto a surface of the sample is equal to or larger than 400 mm and isequal to or smaller than 1500 mm, the distance from the ion source to anend of a side of the sample of the electrostatic lens most proximate tothe ion source is equal to or smaller than 40 mm and the distance froman end of a side of the ion source of the electrostatic lens mostproximate to the sample to a surface of the sample is equal to orsmaller than 40 mm.

Further, the problem is solved by a projection ion beam machiningapparatus which is provided with an electrostatic lens system forforming an ion beam for projection an opening pattern of a mask havingan opening portion onto a sample held by a sample stage, wherein thecurrent density of the ion beam on the sample is equal or larger than 20mA per one square cm.

Furthermore, in the above-described projection ion beam machiningapparatus, the edge resolution power, when the size of the ion beam onthe sample is 5 μm, is equal to or smaller than 0.2 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the total constitution of a projection ionbeam machining apparatus according to the present invention.

FIG. 2 is a perspective view of a sample, a section of which is beingprocessed by a projection ion beam.

FIG. 3 is a diagram showing the operation of an electrostatic deflectorof the projection ion beam machining apparatus according to the presentinvention.

FIG. 4 is a diagram showing a stencil mask of the projection ion beammachining apparatus according to the present invention.

FIG. 5 is a perspective view of a sample, a wall of which is beingformed by a projection ion beam.

FIG. 6 is a diagram showing the total constitute of another embodimentof a projection ion beam machining apparatus according to the presentinvention.

FIGS. 7(a) and 7(b) are perspective views of samples which are beingmachined by a focused ion beam (FIB).

FIGS. 8(a) and 8(b) are diagrams showing a comparison of the operationsof a focused ion beam optical system and a projection ion beam opticalsystem.

BEST MODE FOR CARRYING OUT THE INVENTION

An explanation will be given of the present invention with reference tothe attached drawings in order to describe the present invention infurther detail.

FIG. 1 is a sectional view showing a projection ion beam machiningapparatus according to an embodiment of the present invention. Anapparatus main body 1 is provided with a liquid metal ion source 2 ofGa, a stencil mask 3, an illumination lens 5-1 and a projection lens 5-2which are electrostatic lenses of two stages, and a sample stage 20 formovably holding a sample 6, which are basic constituent elements of theprojection ion beam apparatus. Other than these, there are provided anelectrostatic reflector 8 of two stages, a blanking deflector 9, ablanking aperture 10, a lens condition setting deflector 11 and asecondary electron detector 12. Further, there are provided an electronsource 310 and a gas source 320. In the drawing, a vacuum chambercontaining these elements has been omitted. The ion source 2 isconnected with an acceleration power source 100, and the accelerationvoltage of the ion beam 4 on the sample 6 is determined by the powersource voltage. An electrode 1010 of the illumination lens 5-1 on a sidethereof most proximate to the ion source serves also as an ionextracting electrode and is connected with an ion extracting powersource 101. A power source 102 is connected to a central electrode 1020of an Einzel lens portion of the illumination lens 5-1 and the strengthof the lens can be changed by the power source voltage. A centralelectrode 1030 of the projection lens 5-2 is connected with a lens powersource 103 and the strength of the lens can be changed by the powersource voltage. The mask 3 is exchangeably held by a drive mechanism 111and the drive mechanism 111 is connected with a drive power source 110for selecting one of a plurality of openings on the mask by movementthereof. The electrostatic deflector 8 of two stages is connected with adeflector power source 120. The blanking deflector 9 is connected with adeflector power source 121. The deflector 11 for setting the lenscondition is connected with a deflector power source 122. The secondaryelectron detector 12 is connected with a signal amplifier 130. In thiscase, a beam control circuit 400 can control the acceleration powersource 100, the ion extracting power source 101, the lens power source102, the lens power source 103 and the drive power source 110 and canstore settings for these power sources. Further, a deflector controlcircuit 200 can input a signal from the signal amplifier 130 incooperation with operation of the deflector power source 120 or 122 andcan form a one-dimensional or two-dimensional image and display theimage on a display 201.

Next, an explanation will be given of the operation of the apparatus.The beam amount of the ion beam 4 emitted from the ion source 2 iscontrolled by an ion aperture 7, it is accelerated and focused by theillumination lens 5-1 and it is irradiated onto the stencil mask 3. Inthis case, the acceleration voltage of the ion beam 4 is 30 kV and thecurrent of the extracted ions is 2 μA. Further, the strength of theillumination lens 5-1 is set by the beam control circuit 400 such thatthe ion beam 4 is provided with a minimum beam diameter at the center ofthe projection lens 5-2. Next, the ion beam 4 which has passed throughthe mask 3 is irradiated on the sample 6 held by the sample stage 20 bypassing through the projection lens 5-2. In this case, the strength ofthe projection lens 5-2 is set by the beam control circuit 400 such thatthe ion beam which diverges after passing through an arbitrary point ofthe mask 3 is focused on the sample. Therefore, a pattern of the openingof the mask 3 is projected onto the sample 6 by the ion beam 4 byoperation of the projection lens 5-2.

The most characteristic point of the embodiment resides in the fact thatthe size of the ion optical system significantly differs from an ionoptical system of an FIB apparatus in order to form the projection ionbeam having a high current density. Further, the size significantlydiffers also from the size of an ion optical system of a conventionalprojection ion beam apparatus. That is, whereas the distance L betweenthe centers of the illumination lens 5-1 and the projection lens 5-2 isabout 200 mm in a normal FIB apparatus, in this apparatus, the distanceis about 550 mm, which is twice or more as long as the above-mentionedlength. Further, the distance Lo between the centers of the ion source 2and the illumination lens 5-1 is made as short as about 20 mm. For thispurpose, for the illumination lens 5-1, there is adopted anaxisymmetrical lens having four electrodes integrated with anacceleration lens having two electrodes and an Einzel lens having threeelectrodes (lens in which potentials of electrodes at both ends are thesame) by successively arranging them from the side of the ion source.(One sheet of an electrode connected to the ground is commonlyprovided.) The Einzel lens portion is operated in a deceleration modewhich is liable to constitute a short focus formation. (The lens powersource 102 is a positive power source.) Further, the distance Li betweenthe projection lens 5-2 and the sample 6 is made as short as about 11mm. For that purpose, the electrostatic deflector 8 is arranged on theside of the ion source of the projection lens 5-2 and the space betweenthe sample and the projection lens 5-2 is reduce. Further, for theprojection lens 5-2, there is adopted an Einzel lens operating in adeceleration mode to constitute the projection lens 5-2 as a lens havinga short focus. (The lens power source 103 is a positive power source.)In this case, a distance B between the ion source 2 and the sample 6 is600 mm. Further, the distance A from the ion source 2 to an end of theillumination lens 5-1 on the sample side is 30 mm and the distance Cfrom the sample 6 to an end of the projection lens 5-2 on the side ofthe ion source is 21 mm. Further, (L/Lo)(L/Li) is about 1380. By theabove-described design, according to the apparatus, the pattern of themask 3 can be projected onto the sample 6 by a reduction rate of{fraction (1/45.)} Further, the current density of the ion beam 4 on thesample 6 is 28 mA per 1 square cm.

FIG. 2 shows the result of forming a cross section by the apparatus. Ahole is formed in one operation and at high speed by projecting the ionbeam 4 to a region which is 10 μm square on the sample 6 by using apattern which is 450 μm square on the mask. There is formed a crosssection having inconsiderable edge sagging suitable for observation byan SEM or the like at a wall face of the hole. The current of the ionbeam 4 on the sample is 28 nA and the resolution of the edge in themachining region is about 10 nm. The time period required for forming ahole having a depth of about 10 μm is about 3 minutes. The currentdensity of a FIB is generally about 10 A per 1 square cm and,accordingly, when the beam diameter is set to 0.1 μm, the currentbecomes about 1 nA. When the function of the apparatus is compared withthat of a FIB, not only can the hole be machined at a speed 28 times asfast as that of a FIB, but also the section can be formed with anaccuracy 10 times as high as that of a FIB. In this case, when thesample 6 is an insulating member, by irradiating an electron shower 311from the electron source 310 onto the sample 6, electrification inirradiating the ion beam 4 can completely be prevented. However, whenthe electron shower is used, it is necessary to detect secondary ionsand form an image of the sample by changing the polarity of thesecondary electron detector 12. Further, the flatness of the section canbe improved by machining the hole after piling up a tungsten-like filmby about several thousands nm by irradiating the ion beam 4 onto thesample 6, while blowing gas 321 of tungsten carbonyl W(CO)6 from the gassource 320. Further, when gas of xenon fluoride XeF2 or the like isused, the machining by the ion beam 4 is accelerated in a material of aportion of the sample.

A second characteristic point of the embodiment resides in providingmeans for ensuring that the ion beam is always incident on the centralaxis of the projection lens in order to irradiate the projection ionbeam to an accurate position on the sample by reducing distortion of thepattern. That is, as shown in FIG. 1, the ion beam 4 is deflected toalign with the central axis of the projection lens 5-2 by using the lenscondition setting deflector 11. Further, the position where the ion beam4 is irradiated onto the sample 6 is set with high accuracy bydeflecting the ion beam 4 to always pass through the center of theprojection lens 5-2 by using the electrostatic deflector 8 of twostages. Here, FIG. 3 shows the operation of the projection lens 5-2 ofthe projection ion beam machining apparatus of FIG. 1. The two stagedeflector 8 is constituted by overlapping eight poles electrostaticdeflectors in two stages. Although, according to the deflecting circuit120, the same set voltage is applied to a stage on the side of the ionsource and a stage on the side of sample of the two stage deflector 8,the wirings are connected asymmetrically. The ion beam 4 is made to passalways through the center of the projection lens 5-2 by optimizing aratio of the lengths of the deflectors of two stages. The position atwhich the ion beam 4 is irradiated on the sample 6 can be set within arange of a size of 500 μm square and distortion or blur of the patternis equal to or smaller than 10 m in a range of a radius of 50 μm.According to the conventional projection ion beam apparatus, there beenno example in which the irradiation position call be varied to be largerthan the size of the irradiation pattern. The sample can be machined tohave a shape different from the pattern of the mask by scanning the ionbeam 4 on the sample the deflector 8. Particularly, when the ion beam 4is scanned in parallel with a straight line portion of the pattern ofthe mask, the machining can be carried out without deterioration theedge resolution of the machining region. The same is true with a case inwhich the sample stage 20 is scanned to thereby relatively move the ionbeam 4. Further, conversely, the ion beam 4 can be prevented fromrelatively moving on the sample 6 by moving the sample 6 using thesample stage 20 as the ion beam 4 is moved. In this case, the controlpower source 200 may be provided with a function of adjusting thedeflection voltage of the deflector 8 to correct any variation in theposition of the ion beam 4 relative to the sample stage 20. Further, thelens condition setting deflector 11 is arranged on the ion source sideof the mask 3 to prevent a variation in the size of the pattern of theion beam 4 on the sample 6 by accurately setting the strength of theprojection lens 5-2. In this case, when the ion beam 4 is deflected bythe lens condition setting deflector 11, the pattern of the mask 3 canbe accurately projected onto the sample 6 by setting the strength of theprojection lens 5-2 such that the position of the ion beam 4 is notvaried on the sample 6. This utilizes the fact that when the strength ofthe projection lens 5-2 for projecting the pattern of the mask 3 ispertinently set, the position of the ion beam 4 on the sample 6 is notvaried even in the case in which the position of the ion source 2 iseffectively varied. Here, considering a case in which differentlocations on the sample 6 are continuously machined, when the height ofthe sample is changed, the condition of projecting the projection ionbeam 4 is deviated and the size of the machining pattern is changed. Ittakes time and is not suitable to adjust the strength of the projectionlens 5-2 in the above-described procedure as a countermeasurethereagainst. In this case, the strength of the projection lens 5-2 maybe changed by an amount in proportion to the change in the height of thesample by detecting the change in the height of a portion of the samplefor irradiating the ion beam using a reflected light sensor or the like.It is a well known method to carry out this operation by automaticcontrol.

A third characteristic in the embodiment resides in providing means forcontrolling the time period during which the projection ion beam isirradiated onto the sample with high accuracy. That is, as shown by FIG.3, by deflecting the ion beam 4 as in ion beam 4′ using the blankingdeflector 9 and irradiating the ion beam 4′ onto the blanking aperture10, the ion beam 4′ is cut off from above the sample 6 at high speed. Byarranging the blanking deflector 9 and the blanking aperture 10 on theion source side of the projection lens 5-2, the interval between theprojection lens 5-2 and the sample 6 is minimized. Further, by arrangingthese elements on the sample side of the mask 3, the current of the ionbeam actually irradiated on the sample can be measured at a portion ofthe blanking aperture 10. By calculating the machining speed using thebeam current, the time period during which ions are irradiated on thesample for differing a necessary depth can be accurately calculated. Theblanking deflector 9 is an electrostatic deflector of two poles and theion beam 4 can be fully deflected by a rise time of about 1 μs bysupplying a voltage from the blanking deflector power source 121. Thedeflector power source 121 is controlled by the deflector controlcircuit 200 for controlling the time period during which the ion beam isirradiated on the sample.

A fourth characteristic in the embodiment resides in providing aplurality of selectable openings on the mask and providing the beamcontrol circuit 400 for storing a condition of focusing for an optimumion beam for each of the plurality of openings (lens condition) at astoring portion thereof and arbitrarily changing the condition. Further,there is also provided means for confirming the optimum conditions usingan image of the sample. The more the opening pattern is located towardthe outside of the mask, the more distortion is liable to be caused whenthe pattern is projected on the sample. In order to reduce thedistortion as much as possible, it is necessary to adjust theillumination lens 5-1 such that the ion beam 4 is provided with aminimum beam diameter at the center of the projection lens 5-2. The beamdiameter is controlled by the spherical aberration of the illuminationlens 5-1 and, therefore, the larger the size of the pattern, the morethe strength of the illumination lens 5-1 needs to weaken. In themeantime, in reducing distortion or blur at the central portion of theopening pattern, the strength of the illumination lens 5-1 needs to beoptimized first using a small pattern. A top view of the stencil mask 3in FIG. 1 is shown by FIG. 4. The stencil mask 3 is provided with aplurality of openings. An opening 3-1 and an opening 3-2 are rectangularand are used when the hole for forming the cross section of the sampleshown by FIG. 2 is machined. Angles of the two openings are made todiffer from each other by 45 degrees to align the direction of the crosssection relative to the direction of the semiconductor pattern informing the cross section of a semiconductor sample. In each of anopening 3-4 and an opening 3-5, two rectangles are aligned in linesymmetry. These openings are used for machining holes to form a thinwall in a sample shown by FIG. 5. A closed area 3-7 is used as a shutterfor cutting the ion beam 4. A lens condition is set to each of theseopenings as follows. First, the mask 3 is moved, an opening which isintended for use is set to the center of the ion optical system and theion beam 4 is scanned using the ion beam position adjusting deflector 8.Next, there is observed an image of the sample formed by acquiring anintensity signal of secondary electrons generated from the sample 6 insynchronism with the scanning operation. In this case, the illuminatedlens 5-1 may be adjusted such that a change in solution in the image ofthe sample is minimized while varying the strength of the projectionlens 5-2. However, the strength of the projection lens 5-2 needs to bepertinently set previously. This can simply be set by the followingmethod. First, the mask 3 is moved, a smallest circular opening 3-3 isset to the center of the ion optical system and the ion beam 4 isscanned using the lens condition setting deflector 11. Next, there isobserved the image of the sample formed by acquiring the intensitysignal of the secondary electrons generated from the sample 6 insynchronism with the scanning operation. Here, the projection lens 5-2may be adjusted such that the change in the intensity in the image ofthe sample is minimized. Here, a pertinent rectangular mark is providedon the sample 6 and the position of the ion beam 4 can be calibratedfrom the signal of the secondary electrons provided by scanning the ionbeam 4 on the rectangular mark using the deflector 8. Further, the imageof secondary electrons provided by scanning the ion beam 4 projectingthe smallest circular opening 3-3 on the sample 6 by the deflector 8 isdisplayed on the display 201, and based on the image, the position forirradiating the ion beam at another opening can be designated. Anothersimple method is a method of designating the position for irradiatingthe ion beam using an image of the sample formed by a FIB. First, inFIG. 1, the opening 3-3 of the mask 3 is set to the center of the ionoptical system. Next, the intensities of the illumination lens 5-1 andthe projection lens 5-2 are set such that the image of the ion source 2is projected onto the sample 6. This is the condition for forming a FIB.As mentioned above, the present apparatus is provided with means forstoring the lens condition for each of the openings of the mask andinstantaneously changing the lens condition when needed. By scanning theion beam 4 constituting a FIB on the sample 6 using the deflector 8, theimage of the sample having a high resolution can be formed by secondaryelectrons generated from the sample. Although there is a restriction inthe machined shape in the ion beam projecting the pattern of the mask,when a FIB is formed by changing the lens condition as mentioned above,the sample can be machined successively in an arbitrary shape.

FIG. 6 is a diagram of a projection ion beam machining apparatusaccording to a second embodiment of the present invention. The apparatusmain body I is provided with the liquid metal ion source 2 of Ga, thestencil mask 3, an illumination lens 5-1 comprising three electrostaticlenses, a first projection lens 5-2 and a second projection lens 5-3 anda sample stage 20 for movably holding a sample 6, which are basicconstituent elements of the projection ion beam apparatus. Otherthanthese, there are provided an electrostatic deflector 8 of two stages, ablanking deflector 9, a blanking aperture 10, a lens condition settingdeflector 11 and a secondary electron detector 12. Further, there areprovided a fixed aperture 13, an alignment deflector 14, a movableaperture 15 and a contamination preventive aperture 300. A vacuumchamber containing these elements is omitted in the drawing. The ionsource 2 is connected with an acceleration power source 100. Theacceleration voltage of the ion beam 4 on the sample 6 is determined bythe voltage of the acceleration power source 100. The electrode 1010 onthe side of the illumination lens most proximate to the ion sourceservices also as the electrode for extracting ions, which electrode isconnected to the ion extracting power source 101. The lens power source102 is connected to the central electrode 1020 of the Einzel lensportion of the illumination lens 5-1 and the strength of the lens ischanged by the power source voltage. The central electrode 1030 of theprojection lens 5-2 is connected with the lens power source 103 and thestrength of the lens is changed by the power source voltage. A centralelectrode 1040 of the projection lens 5-3 is connected with a lens powersource 104 and the strength of the lens is changed by the power sourcevoltage. The mask 3 is movably held by the drive mechanism 111, which isconnected with the drive power source 110 for selecting one of aplurality of openings on the mask. The movable aperture 15 is connectedwith a drive mechanism 113, which receives power from a drive powersource 112. The electrostatic deflector 8 of two stages is connectedwith the deflector power source 120. The blanking deflector 9 isconnected with the deflector power source 121. The lens conditionsetting defector 11 is connected with the deflector power source 122.The alignment deflector 14 is connected with a deflector power source123. The secondary electron detector 12 is connected with the signalamplifier 130. In this case, the beam control circuit 400 can controlthe acceleration power source 100, the ion extracting power source 101,the lens power source 102, the lens power source 103, the lens powersource 104 and the drive power source 110 and can store the settings ofthese power sources. Further, the deflector control circuit 200 caninput a signal from the signal amplifier 130 in cooperation with theoperation of the deflector power source 120, the deflector power source122 or the deflector power source 123 and can form a one-dimensional ortwo-dimensional image and display the image on the display 201.

Next, an explanation will be given of the operation of the apparatus.The beam amount of the ion beam 4 emitted from the ion source 2 iscontrolled by the ion aperture 7, the ion beam 4 is accelerated andfocused by the illumination lens 5-1 and is irradiated onto the stencilmask 3. In this case, the acceleration voltage of the ion beam 4 is 30kV and the current for extracted ions is 2 μA. Further, the strength ofthe illumination lens 5-1 is set by the beam control circuit 400 suchthat the ion beam 4 is provided with a minimum beam diameter at thecenter of the fixed aperture 13. Further, the strength of the projectionlens 5-3 is set by the beam control circuit 400 such that the ion beam 4is provided with a minimum beam diameter at the center of the projectionlens 5-2. Next, the ion beam 4 which has passed through the mask 3 isfocused by the projection lens 5-2 and the projection lens 5-3 and isirradiated onto the sample 6. In this case, the projection lens 5-2 andthe projection lens 5-3 are set by the beam control circuit 400 suchthat the ion beam which passes through an arbitrary point on the mask 3and is diverged is focused on the sample. As mentioned above, thepattern of the opening of the mask 3 is projected onto the sample 6 bythe ion beam 4.

The first characteristic point of the embodiment resides in using threeelectrostatic lenses. Thereby, in comparison with the projection ionbeam machining apparatus according to Embodiment 1, a projection ionbeam can be formed which has a higher current density. In the projectionion beam optical system using two lenses, as shown in FIG. 8(b), when Lis simply prolonged in order to increase the current density, adjustmentof the strength of the electrostatic lens 1 becomes delicate. That is,high resolution is needed in setting the voltage of the electrostaticlens. Actually, there is needed an accuracy equal to or lower than 10 μmin setting L, however, when L exceeds 1000 mm, the situation becomesdifficult to deal with by an ordinary high voltage power source and theresolution of the digital analog converter (DAC). Hence, according tothe embodiment, as shown in FIG. 6, the operation of focusing the ionbeam 4 to the center of the first projection lens 5-2 is carried out byallotting the operation to the illumination lens 5-1 and the addedsecond projection lens 5-3. Thereby, resolutions necessary for settingthe voltage to the respective lenses are brought into practical ranges.In this case, the distance B between the ion source 2 and the sample 6is 600 mm. Further, the distance A from the ion source 2 to the end ofthe sample side of the illumination lens 5-1 is 31 mm and the distance Cfrom the sample 6 to the end of the ion source side of the projectionlens 5-2 is 21 mm. Although the distance L between the centers of theillumination lens 5-1 and the projection lens 5-2 is about 550 mm, aneffective value of L (L for providing a similar function using lenses oftwo stages) is 1250 mm. Further, although (L/Lo)(L/Li) is about 2290,the value is about 11900 effectively. By the above-described design,according to the apparatus, the pattern of the mask 3 can be projectedonto the sample 6 by a reduction rate of {fraction (1/100)} and thecurrent density of the ion beam 4 on the sample 6 is 400 mA per 1 squarecm. Further, there is a possibility of shifting the optical axis sincethe number of lenses is increased to three stages, and, accordingly, itis preferably to provide the alignment deflector 16 for the correction.

An explanation will be given of the procedure for forming a wall-likestructure for TEM observation on the sample, as shown in FIG. 5. A wallstructure having a length of 3 μm and a width of 0.1 μm can be formed inone operation and at high speed by projecting two rectangular patternseach having a size of 300 μm×200 μm square, which are arranged at aninterval of 10 μm on the mask, onto the sample 6 using the ion beam 4.The current of the ion beam 4 on the sample 6 is 48 nA and theresolution of an edge of a machining region is about 20 nm. The timeperiod required for forming a hole having a depth of about 10 μm isabout 3 minutes. When such a high speed machining is continuouslycarried out, a large amount of the substances sputtered from the sample6 adhere to the contamination preventive aperture 300 in FIG. 6. Whenthe sample 6 is provided with an insulating property, there is apossibility that the position of the ion beam 4 will be changed due toelectrification by the adhered substances. Therefore, the contaminationpreventive aperture 300 is grounded and is installed such that thesingle member aperture can pertinently be interchanged.

Further, in FIG. 6, even when the stencil mask 3 is provided at theposition of the movable aperture 15, the projection ion beam 4 having asimilar current density can be formed by pertinently setting thestrength of the projection lens 5-2. However, in that case, patterns onthe stencil mask need to have smaller sizes. Further, in FIG. 6 a FIBcan be formed by adjusting the illumination lens 5-1, the illuminationlens 5-2 and the illumination lens 5-3 to pertinent intensities. In thiscase, a slender FIB can be formed by restriction the ion beam 4 usingthe movable aperture 15.

A second characteristic point of the embodiment resides in using aspecial constitution in the first stage of the electrostatic lens.Thereby, in comparison with the projection ion beam machining apparatusof Embodiment 1, there can be formed a projection ion beam having ahigher current density. In FIG. 1, when the illumination lens 5-1 isproximate to the ion source 2 to thereby reduce Lo, the aperture 7 alsobecomes necessarily proximate to the ion source 2 and in accordancetherewith, the possibility that back-sputtered particles or secondaryelectrons emitted from the aperture 7 reach a front end of the ionsource 2 is also increased. This effects enormous adverse influence onion emission stability and the lift of the ion source 2. Therefore, alower limit of the distance between the ion source 2 and the aperture 7is about 5 mm and a lower limit of Lo is about 15 mm. Hence, accordingto the embodiment, as shown by FIG. 6, the illumination lens 5-1 isconstituted by an acceleration lens having two electrodes and an Einzellens having three electrodes and the aperture 7 is arranged betweenthese lenses. Further, the aperture 7 is connected to a constant voltagecircuit 70 to thereby bias it to about 50 V and prevent emission ofsecondary electrons. Thereby, according to the embodiment, the distanceLo between the ion source 2 and the illumination lens 5-1 can beshortened to about 12 mm and further, the distance between the ionsource 2 and the aperture 7 can be increased to 10 mm.

As described above, the projection ion beam machining apparatusaccording to the present invention is useful for applications in which aregion having a size equal to or smaller than several 10 μm is machinedwith an accuracy of sub μm at high speed and is particularly suitablefor applications in which high accuracy is particularly required at aside of a portion of a machining region, as in observation of a sectionof a semiconductor or the like.

Further, the projection ion beam machining apparatus according to thepresent invention is applicable also to a machining operation, thereduction to practice of which has been difficult due to the problem ofthroughput in the conventional focused ion beam machining apparatus.

What is claimed is:
 1. A projection ion beam machining apparatuscomprising: an ion source, a sample stage for holding a sample to bemachined, a stencil mask including an opening through which an ion beamfrom the ion source passes, an illumination lens arranged between theion source and the stencil mask, a projection lens arranged between thestencil mask and the sample stage, a power source connected to theillumination lens, and means for controlling the illumination lens,wherein said means for controlling the illumination lens controls avoltage of the power source to minimize a diameter of the ion beam at acenter of the projection lens.
 2. The projection ion beam machiningapparatus according to claim 1, wherein said illumination lens and saidprojection lens each comprise electrostatic deflecting means.
 3. Theprojection ion beam machining apparatus according to claim 1, whereinsaid illumination lens comprises an Einzel lens.
 4. The projection ionbeam machining apparatus according to claim 1, further comprising: anblanking deflector arranged on a side of the ion source of theprojection lens for blanking an ion beam, and a fixed aperture arrangedon a side of the sample stage of the blanking deflector.
 5. Theprojection ion beam machining apparatus according to claim 1, furthercomprising: a plurality of selectable operable openings in the stencilmask, said means for controlling the illumination lens comprising: meansfor storing two or more sets of control parameters, and means forchanging the sets of the control parameters in association with a changeof the openings of the mask.
 6. The projection ion beam machiningapparatus according to claim 1, wherein a value of (L/Lo)(L/Li) is equalto or larger than 400, where the Lo is defined as a distance from asubstantial center of the illumination lens most proximate to the ionsource and an ion emitting portion of the ion source, the Li is definedas a distance between a substantial center of the projection lens mostproximate to the sample and a surface of the sample, L is defined as adistance between the substantial centers of the illumination lens andthe projection lens.
 7. A projection ion beam machining apparatuscomprising: an ion source, a stage to hold a sample, a mask having anopening to pass an ion beam; an illumination lens arranged between theion source and the mask, a projection lens arranged between the mask andthe stage, a power source coupled to the illumination lens, and meansfor controlling the illumination lens and controlling a voltage of thepower source so as to minimize a diameter of the ion beam at a center ofthe projection lens.
 8. The projection ion beam machining apparatusaccording to claim 7, wherein said illumination lens and said projectionlens each comprise electrostatic deflecting means.
 9. The projection ionbeam machining apparatus according to claim 7, wherein said illuminationlens comprises an Einzel lens.
 10. The projection ion beam machiningapparatus according to claim 7, further comprising: a blanking deflectorarranged on a side of the ion source of the projection lens to blank anion beam; and a fixed aperture arranged on a side of the stage of theblanking deflector.
 11. The projection ion beam machining apparatusaccording to claim 7, further comprising: a plurality of selectableopenings in the mask, said means for controlling the illumination lenscomprising: means for storing a plurality of sets of control parameters,and means for changing the control parameters in association with achange of said openings.
 12. The projection ion beam machining apparatusaccording to claim 7, wherein a value of (L/Lo)(L/Li) is equal to orlarger than 400, where, the Lo is a distance from a substantial centerof the illumination lens most proximate to the ion source and an ionemitting portion of the ion source, the Li is a distance between asubstantial center of the projection lens most proximate to the sampleand a surface of the sample, L is a distance between the substantialcenters of the illumination lens and the projection lens.